1. Field of the Invention
The present invention relates to a battery charger for charging rechargeable secondary batteries, such as nickel-cadmium batteries, lithium-ion batteries.
2. Description of the Related Art
Rechargeable secondary batteries have been widely used as a power source of portable devices, such as a cordless power tools. Conventional battery chargers for charging such secondary batteries are, in use, connected to a commercial power supply. However, when the cordless power tool is used in places where the commercial power supply is not available, the user has to bring extra batteries for replacement with the empty batteries.
To resolve the above-mentioned problem, Japanese Patent Application Publication No. 2005-245145 proposes a battery charger capable of charging secondary batteries while being supplied with power from various types of power supplies including the commercial power supply.
However, the battery charger disclosed in Japanese Patent Application Publication No. 2005-245145 accommodates a plurality of power source circuits corresponding to the number of available power supplies, so that the size of the battery charger becomes large. In addition, the secondary batteries charged by the battery charger disclosed in Japanese Patent Application Publication No. 2005-245145 are overcharged when a particular power supply is used. The secondary batteries might be physically destroyed or generate an undue amount of heat due to overcharging. Hence, battery chargers capable of safely charging the batteries have been sought in the art.